All previous investigations have reported so large a percentage of "false abnormal" electrocardiographic (ECG) responses to exercise in women that the value of the ECG exercise test is women for the recognition of coronary insufficiency is seriously limited. However, the same ECG criteria were used for men and women, which is incorrect. It is proposed to determine the normal 95 percentile range limits of the ECG response to a standardized exercise test (progressive exercise on a treadmill up to 85 percent of max. VO2, predicted from the age-corrected heart rate). The upper (97.5 percent) and lower (2. 5 percent) limits will be determined on the basis of the distribution of the various ECG items, particularly ST-T changes, in a sample of 300 healthy women from 20 to 65 years. It is proposed to repeat the test after an interval of several months in about one third of the sample. A control group of 150 healthy men from 40 to 60 years will also be investigated. On the basis of existent information, larger ST-T changes must be expected in women. In men, the value of the ECG exercise test for prediction of morbidity and mortality of coronary artery disease has been firmly established. It is expected that the sex-corrected standards resulting from this study will contribute to make the ECG exercise test as valuable in women as in men. In addition, it is proposed to compare the ECG responses to exercise in about 125 men and 125 women with similar degree of coronary heart disease, based on independent clinical information, including coronary arteriography in an appreciable number of patients. The purpose of this ancillary project is validation of the normal limits in clinical application.